In existing magnetic tape cartridges, which are being used as_storage media employed in external storage units for computers, etc., there is known a type where a single reel with magnetic tape wound thereon is rotatably housed within a cartridge case. This magnetic tape is employed to archive data for computers, etc. Since important information has been stored, the magnetic cartridge is constructed so that problems, such as tape jamming, etc., do not occur and that the magnetic tape is not pulled out of the cartridge case unexpectedly.
Also, as shown in FIGS. 1, 4, etc., of Japanese Unexamined Patent Publication No. 11(1999)-232838, a leader pin (tape pulling-out tool) is affixed to the leading end portion of the magnetic tape to pull the magnetic tape out of the cartridge case. This leader pin is held and pulled out by a hold member of a drive unit provided on the side of a recording-reproducing apparatus, whereby forward winding or reverse winding of the magnetic tape is performed. Uniting of the leader pin and the magnetic tape can be performed by winding the magnetic tape on the outer periphery of the tape clamp shaft portion of the leader pin and then elastically fitting a clamp member with a C cross section onto the tape clamp portion to clamp the leading end portion of the magnetic tape therebetween.
In the structure in which the leader pin is affixed to the leading end of magnetic tape as described above, the coefficient of friction between the magnetic tape and the leader pin is low and therefore there is a possibility that because of insufficient clamping force, the leader pin will be disengaged from the magnetic tape.
More specifically, in order to reduce the sliding friction between the magnetic tape and the magnetic head, there are cases where the addition of a lubricating agent to the magnetic layer of the magnetic tape, or the coating of a lubricating agent on the top surface of the magnetic tape, is performed so that the coefficient of friction is reduced. The bottom surface of the magnetic tape is also treated in the same manner. In that case, the coefficient of friction between the leader pin, formed from stainless steel, etc., and the magnetic tape varies with the type of the magnetic tape. When this coefficient of friction is low, there are cases where the clamping force of the magnetic tape with respect to the leader pin by the engagment of the clamp member onto the leader pin is reduced.
The present invention has been made in view of the points mentioned above. Accordingly, it is a primary object of the present invention to provide a magnetic tape cartridge that is capable of enhancing the clamping force of the magnetic tape with respect to the leader pin to assure reliability.
The aforementioned leader member is detachably held in the cartridge case by a lock member, called a shaft holding portion, which has an engaging function, as shown in FIG. 6 of the aforementioned Japanese Unexamined Patent Publication No. 11(1999)-232838. It is advantageous from the viewpoint of structural simplification to employ a spring member to hold the leader member.
Therefore, if there is provided a lock member with integral upper and lower hold portions which abut the upper and lower ends of the leader pin, the assembly of the leader pin to the upper and lower cases of the magnetic tape cartridge will be enhanced. However, in forming the lock member by stamping and bending a plate spring, the manufacturing precision is reduced depending on the configuration of the lock member and there is a problem that the holding force of the lock member with respect to the leader pin will vary.
For example, consider a lock member manufactured by pressing a plate spring such as that shown in FIGS. 15 and 16. In FIG. 15, a leader pin 5 affixed to the leading end of magnetic tape 6 is pulled in and out through an opening 10 formed in the side surfaces of an upper case (not shown) and a lower case 3. Inside the opening 10, upper and lower housing recesses 20 are formed in the bottom surface of the upper case and the top surface of the lower case 3, and the upper and lower end portions of the leader pin 5 are held in the housing recesses 20. Also, a tapered lower guide portion 21 is provided from the lower housing recess 20 toward the opening 10. A lock member 50, for detachably holding the leader pin 50 in the housing recesses 20, is symmetrical in the vertical direction thereof and formed into a U-shape, as shown in FIG. 16. The lock member 50 has a mounting portion 50a, which is clamped between a mounting boss 51 erected in the bottom surface of the lower case 3 and the side wall 3b of the lower case 3, along the side wall 3b. The lock member 50 also has upper and lower elastic arm portions 50b, 50b extending from the forwardly curved rear portion of the mounting portion 50a toward the opening 10. The elastic arm portions 50b, 50b have leader-pin holding portions 50c, 50c at their outer ends, respectively. The leader-pin holding portions 50c, 50c abut the upper and lower end portions of the leader pin 5, respectively. Each leader-pin holding portion 50 is bent and has an outer inclined surface which is contacted and deformed by the leader pin 5 being inserted through the opening 10, and an inner inclined surface with which the leader pin is pressed against and held in the housing recess 20.
The lock member 50 is bent into a deeply curved U-shape by pressing a plate spring, so it is difficult to accurately form an angle α (see FIG. 16) which the mounting portion 50a forms with the elastic arm portion 50b. The amount of deformation in pressing and holding the leader pin 5 varies and therefore the holding force of the lock member 50 with respect to the leader pin 5 tends to vary. In addition, the deep U-shape pressing requires a plurality of press operations and increases the number of manufacturing steps. Since the deep U-shape pressing makes the length of the elastic arm portion 50b longer and thus increases the developed area, a large quantity of plate spring material is discarded after the stamping operation. Thus, the deeply U-shaped lock member 50 is disadvantageous in terms of cost. Furthermore, when a large number of lock members 50 are stored, they are stacked and engaged with one another, if each lock member 50 has a deeply curved U-shape. Since it is difficult to separate them from each other, there is the problem that feeding them serially by a part feeder may become difficult.
On the other hand, in the mounting structure of the lock member 50 in the cartridge case 4, in which the mounting portion 50a of the lock member 50 is disposed along the side wall 3b of the lower case 3 and clamped between the side wall 3b and the mounting boss 51, that part of the metal mold which molds the gap between the mounting boss 51 and the side wall 3b will become very thin, if the lock member 50 is made thin in order to obtain proper leader-pin holding force. Because of this, there is a possibility that the thickness-reduced part of the metal mold will be damaged by pressure produced when resin is injected. It is also difficult to manufacture a metal mold having thin portions. Particularly, when the mounting boss 51 is formed high, or long along the side wall 3b, the aforementioned phenomenon becomes conspicuous.
Furthermore, when the plate-shaped lock member 50 is assembled into the cartridge case 4, depending on the locking structure there is a possibility that the upper case cannot be closed to the lower case 3. That is, when the lock member 50 is set to the lower case 3, and the upper case is stacked on the lower case 3, the lock member 50 tilts and cannot engage with the mounting boss 51 of the upper case and abut the lower end of the mounting boss 51, and therefore the upper case cannot be closed. Particularly, a space is required around the leader pin 5 so that a leader-pin pulling-out mechanism of a drive unit can enter through the opening 10 and hold the leader pin 5. The mounting boss 51 needs to be low in height so that it does not interfere with the leader-pin pulling-out mechanism, and the mounting boss also cannot be made high from the viewpoint of the metal-mold strength described above. Therefore, there is a possibility that problems associated with the aforementioned tilting will arise.
The present invention has been made in view of the points mentioned above. Accordingly, it is a secondary object of the present invention to provide a magnetic tape cartridge which is capable of holding the leader pin in a satisfactory manner by improving the manufacturing precision, mounting performance, etc., of the spring member which detachably holds the leader pin.